Tissue-specific androgen-inhibited gene expression of a submaxillary gland protein, a rodent homolog of the human prolactin-inducible protein/GCDFP-15 gene.

The human PRL-inducible protein (PIP)/gross cystic disease fluid protein-15 is expressed in pathological conditions of the mammary gland and in several exocrine tissues, such as the lacrimal, salivary, and sweat glands. In human breast cancer cells, the expression of PIP/gross cystic disease fluid protein-15 is stimulated by androgen and PRL, and inhibited by estrogen. However, it is not known whether the expression of PIP in other tissues is under similar hormonal regulation. In the present study we employed reverse transcriptase-polymerase chain reaction followed by rapid amplification of complementary DNA (cDNA) ends to amplify the PIP cDNA homolog, the submaxillary gland protein (SMGP) in the mouse. The mouse PIP/SMGP cDNA encodes a putative secreted peptide of 144 amino acids with a 51% identity with human PIP. Using the mouse PIP/SMGP cDNA as a probe, we examined the tissue- and cell-specific expression of PIP/SMGP messenger RNA by in situ hybridization and Northern blot analysis of mouse and rat tissues. Hormonal regulation was also studied in the rat. PIP/SMGP messenger RNA expression was only detected in the lacrimal and submaxillary glands of the rodents. In the rat submaxillary gland, PIP/SMGP gene expression was confined to the acinar cells. In the male rat lacrimal gland, castration resulted in an increase in expression, and in both male and female rats, androgen replacement abolished PIP/SMGP gene expression. This pattern of regulation was not observed in the submaxillary gland and was actually reversed in human breast cancer cells. PRL had no effect on the regulation of PIP/SMGP in either salivary or lacrimal glands. Our study indicates that tissue-specific factors are important in determining the hormone responsiveness of the PIP/SMGP gene. Regulation of the PIP/SMGP gene in vivo may provide a useful model system to study the mechanism of down-regulation of expression by androgen in a tissue-specific manner.